1. Field of the Invention
The present invention relates to a motor controller, and more particular to a motor controller for accumulating electrical energy in a capacitor during deceleration of a motor and for supplying the electrical energy accumulated in the capacitor during acceleration of the motor.
2. Description of Related Art
A driving apparatus is known that includes a motor controller having a converter for receiving an AC voltage and performing AC-to-DC power conversion thereon, an inverter for receiving a DC voltage and performing DC-to-AC power conversion thereon, and a capacitor and a charging/discharging control circuit connected in parallel with a DC link between the converter and the inverter. Under the control of the charging/discharging control circuit, electrical energy is charged to the capacitor and the electrical energy accumulated in the capacitor is discharged.
In a driving apparatus of this type disclosed in JP 2000-141440A, electrical energy is supplied from the capacitor to the DC link when a voltage across the capacitor is equal to or higher than a DC link voltage of the DC link. FIGS. 25a and 25b show a relation between motor speed, DC link voltage, and capacitor voltage in the prior art motor controller.
The above-described conventional motor controller operates to supply electrical energy from the capacitor to the DC link when the capacitor voltage is equal to or higher than the DC link voltage of the DC link. When the capacitor voltage is lower than the DC link voltage, electrical energy cannot be supplied from the capacitor to the DC link.
With the prior art motor controller, the capacitor can only be discharged up to the DC link voltage as shown in FIGS. 25a and 25b. Thus, energy able to be discharged by the capacitor is small. When a difference between the capacitor voltage and the DC link voltage becomes small, the response of current supply to load change is deteriorated.